Search for a command to run...
I love teaching & accelerating people's learning. My goal is to unveil complex topics & leave my readers feeling enabled.
I think many members of the developer community act as "gatekeepers" to knowledge. This discourages people from improving themselves at times when they need encouragement the most. I hope to decrease this feeling & encourage people that they are capable of learning new & challenging concepts.
I look forward to sharing my knowledge & I hope what I share helps :)
No comments yet. Be the first to comment.
This post is a brief overview of how Python evaluates the truthiness of objects. In Python, any object can be tested for truth value!
The following built-in objects evaluate to False:
constants defined to be false: None and False.
zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)
empty sequences and collections: '', (), [], {}, set(), range(0)
If a built-in object is not one of these values, it will evaluate to True. Below are examples of what some built-in objects evaluate to (the bool() method is a built-in method used to evaluate the truth value of objects):
bool(0)
False
bool(5)
True
bool([])
False
bool('hello')
True
bool(None)
False
Non built-in objects are evaluated to True by default.
class Book:
def __init__(self, pages: int) -> None:
self.pages = pages
book_1 = Book(100)
bool(book_1)
True
To override this default behavior, the __bool__ method can be defined within a class. Within this dunder method, conditions can be set for when an object evaluates to True or False.
class Book:
def __init__(self, pages: int) -> None:
self.pages = pages
def __bool__(self) -> bool:
if self.pages < 0:
return False
return True
book_1 = Book(100)
book_2 = Book(-100)
bool(book_1)
True
bool(book_2)
False
If the __bool__ method is not defined, Python will then look for the __len__ method within the class. If the __len__ method is defined, then an object will evaluate to False if the __len__ method would return a value of 0 for that object.
class Book:
def __init__(self, pages: int) -> None:
self.pages = pages
def __len__(self) -> int:
return self.pages
book_1 = Book(100)
book_2 = Book(0)
bool(book_1)
True
bool(book_2)
False
In summary, the __bool__ method will take precedence over the __len__ method if both are defined in a class. If neither the __bool__ nor __len__ method are defined, all objects of the class will evaluate to True.
Functions & methods, as objects, will always evaluate True.
class Book:
def __init__(self, author: str, available: bool, pages: int) -> None:
self.available = available
self.author = author
self.pages = pages
def set_to_unavailable(self) -> None:
self.available = False
def indepedent_function() -> None:
print('I am a function.')
book_1 = Book('Mitch', True, 100)
bool(book_1.available)
True
bool(indepedent_function)
True
Hopefully this article has clarified how Python evaluates the truthiness of objects!